Nephropathic cystinosis is an autosomal, recessively inherited storage disease in which nonprotein cystine accumulates within cellular lysosomes due to a defect in lysosomal cystine transport. Ocular manifestations include photophobia crystal deposits in cornea, conjunctiva, iris and depigmentation of the retina. Systemic complications include the Fanconi syndrome, and renal failure. Eight years ago cysteamine, a free thiol which depletes cystine from cells, was introduced in the therapy of cystinotic patients. Although patients had improved growth and stabilized renal function, there was no noticeable effect on the accumulation of corneal crystals. Recent studies showed that corneal cells in tissue culture are readily depleted of cystine by the introduction of cysteamine, making feasible the use of topical ophthalmic cysteamine to circumvent the humoral route. After appropriate animal studies to test for complications which revealed none, we have begun a double-masked clinical trial to test the efficacy of topical cysteamine (0.1%) in humans. Sixteen patients have thus far been enrolled. Four patients have shown significant decrease in the cysteamine treated eyes and are now taking drops in both eyes. To permit increasing the concentration of cysteamine eye drops in humans, a study was performed in rabbits, permitting an increase in the concentration to 0.5%.